Partial spacer for increasing self aligned contact process margins

ABSTRACT

A semiconductor structure is provided. The semiconductor includes a gate stack on a substrate. The semiconductor includes a first set of sidewall spacers on opposite sidewalls of the gate stack. The semiconductor includes a flowable dielectric layer on the substrate, covering at least a portion of the first set of sidewall spacers. The semiconductor includes a second set of sidewall spacers next to the first set of sidewall spacers covering an upper portion thereof, the second set of sidewall spacers are directly on top of the flowable dielectric layer. The semiconductor includes a contact next to at least one of the second set of sidewall spacers.

BACKGROUND

The present invention generally relates to semiconductor devicemanufacturing, and more particularly to fabricating semiconductordevices having spacer for increasing self aligned contact processmargins.

Contacts may be formed in order to make electrical connections to asemiconductor device. Contacts to a source region or a drain region ofthe semiconductor device may be referred to as CA contacts. CA contactsmay be distinguished from CG contact which may form an electricalconnection to a gate conductor of a semiconductor device. The source anddrain regions must remain electrically insulated from the gate terminalin order to maintain functionality of the semiconductor device.Conversely, a short circuit between the source and drain regions and thegate terminal may damage the semiconductor device. A CA contact may beformed in a contact hole etched in a contact-level dielectric, andtherefore would be surrounded by the contact-level dielectric. Selfaligned contact (SAC) process may include CA contact, which canpartially overlap the gate conductor.

SUMMARY

According to one embodiment, a semiconductor structure is provided. Thesemiconductor includes a gate stack on a substrate. The semiconductorincludes a first set of sidewall spacers on opposite sidewalls of thegate stack. The semiconductor includes a flowable dielectric layer onthe substrate, covering at least a portion of the first set of sidewallspacers. The semiconductor includes a second set of sidewall spacersnext to the first set of sidewall spacers covering an upper portionthereof, the second set of sidewall spacers are directly on top of theflowable dielectric layer. The semiconductor includes a contact next toat least one of the second set of sidewall spacers.

According to another embodiment, a method is provided. The methodincludes forming a gate stack on a substrate, the gate stack comprisinga gate cap and a gate with the gate cap located above and in directcontact with the gate. The method further includes forming sidewallspacers along opposite sidewalls of the gate stack, each of the sidewallspacers comprising an upper portion and a lower portion, the upperportion having a width greater than the lower portion.

According to yet another embodiment, a method is provided. The methodincludes forming dummy gate stack on a semiconductor substrate. Themethod further includes forming a first set of sidewall spacers onopposite sidewalls of the dummy gate stack. The method further includesdepositing a first flowable dielectric layer directly on thesemiconductor substrate causing the first set of sidewall spacers beingembedded inside said first flowable dielectric layer. The method furtherincludes exposing an upper portion of the first set of sidewall spacersby recessing the first flowable dielectric layer. The method furtherincludes forming a second set of sidewall spacers next to the first setof sidewall spacers covering the upper portion thereof, the second setof sidewall spacers are directly on top of the flowable dielectriclayer. The method further includes depositing a second flowabledielectric layer on top of the first flowable dielectric covering thedummy gate stack, the first set of sidewall spacers, and the second setof sidewall spacers. The method further includes exposing the dummy gatestack by polishing the second flowable dielectric layer. The methodfurther includes replacing the dummy gate stack with a metal gate stack.The method further includes depositing a third flowable dielectric layeron top of the second flowable dielectric layer covering the metal gatestack, the first set of sidewall spacers, and the second set of sidewallspacers. The method further includes forming a contact adjacent to themetal gate stack in direct contact with the second set of sidewallspacers but not in direct contact with at least a lower portion of thefirst set of sidewall spacers.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following detailed description, given by way of example and notintend to limit the disclosure solely thereto, will best be appreciatedin conjunction with the accompanying drawings, in which:

FIG. 1, an intermediate step in the fabrication of the structure 100,according to an embodiment.

FIG. 2, a first flowable dielectric layer 130 is deposited on top of thestructure 100, according to embodiments.

FIG. 3, is a conformal dielectric layer 140 may be deposited on top ofstructure 100, according to embodiments.

FIG. 4 is a demonstrative illustration of a structure after processsteps of etching the conformal dielectric to form a partial spacer,according to embodiments.

FIG. 5 is a demonstrative illustration of a structure after processsteps of a chemical mechanical polishing (CMP) technique and replacementof a dummy gate with a metal gate, according to an embodiments.

FIG. 6 a demonstrative illustration of a structure after process stepsof recessing of a metal gate and a gate dielectric and formation of agate cap 165, according to embodiments.

FIG. 7 is a demonstrative illustration of the structure after processsteps of etching a contact hole, according to embodiments.

DETAILED DESCRIPTION

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it can be understood that the disclosed embodiments aremerely illustrative of the claimed structures and methods that may beembodied in various forms. This invention may, however, be embodied inmany different forms and should not be construed as limited to theexemplary embodiments set forth herein. Rather, these exemplaryembodiments are provided so that this disclosure will be thorough andcomplete and will fully convey the scope of this invention to thoseskilled in the art. In the description, details of well-known featuresand techniques may be omitted to avoid unnecessarily obscuring thepresented embodiments.

References in the specification to “one embodiment”, “an embodiment”,“an example embodiment”, etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the disclosed structures andmethods, as oriented in the drawing figures. The terms “overlying”,“atop”, “on top”, “positioned on” or “positioned atop” mean that a firstelement, such as a first structure, is present on a second element, suchas a second structure, wherein intervening elements, such as aninterface structure may be present between the first element and thesecond element. The term “direct contact” means that a first element,such as a first structure, and a second element, such as a secondstructure, are connected without any intermediary conducting, insulatingor semiconductor layers at the interface of the two elements.

In the interest of not obscuring the presentation of embodiments of thepresent invention, in the following detailed description, someprocessing steps or operations that are known in the art may have beencombined together for presentation and for illustration purposes and insome instances may have not been described in detail. In otherinstances, some processing steps or operations that are known in the artmay not be described at all. It should be understood that the followingdescription is rather focused on the distinctive features or elements ofvarious embodiments of the present invention.

It should be noted that the invention disclosed below may be fabricatedusing either a replacement gate or gate last process flow, or a gatefirst process flow. A replacement gate process flow will be relied onfor the description provided below.

In a replacement gate (RG) fabrication approach, a semiconductorsubstrate may be patterned and etched to form fins. Next, a dummy gatemay be formed in a direction perpendicular to the length of the fins.For example, the dummy gate may be pattered and etched from apolysilicon layer. A pair of sidewall spacers can be disposed onopposite sidewalls of the dummy gate. The dummy gates and the pair ofsidewall spacers may then be surrounded by an inter-level dielectric.Later, the dummy gates may be removed from between the pair of sidewallspacers, as by, for example, an anisotropic vertical etch process suchas a reactive ion etch (RIE). This creates an opening between the pairof sidewall spacers where a metal gate may then be formed between thepair of sidewall spacers. Optionally, a gate dielectric may beconfigured below the metal gate.

In such cases, the etching technique used during the self alignedcontact processing may consume a portion of a sidewall spacer and aportion of a gate cap, both typically made from nitride. Furthermore,the interface between the sidewall spacer and the gate cap may etchfaster resulting in a stepped profile. Depending on gate-contactalignment, etch chemistry, and etch process details, the etchingtechnique used can result in a short between the gate and the selfaligned contact if the sidewall spacer and/or the gate cap are eroded orconsumed to where the conductive material of the gate is exposed.

Embodiments of the present invention generally relate to semiconductordevice manufacturing, and more particularly to fabricating semiconductordevices having an additional spacer for increasing the process marginfor fabricating self-aligned contacts. One technique may includefabricating the additional spacer adjacent to an existing sidewallspacer of a semiconductor device. The additional spacer mayalternatively be referred to as a knee spacer. One embodiment by whichto fabricate the additional spacer and increase the process margin forfabricating self aligned contacts is described in detail below byreferring to the accompanying drawings FIGS. 1-7.

FIGS. 1-7 illustrate and describe stages in a fabrication process of asemiconductor structure 100 (hereinafter “structure”), in accordancewith an embodiment of the invention. Each of the figures is a crosssection of a portion of the structure 100, such as, for example, aportion of a wafer, a die, or a region thereof.

Referring now to FIG. 1, an intermediate step in the fabrication of thestructure 100, according to an embodiment, is shown, and will bedescribed in detail. The structure 100 may include dummy gate 114,dielectric layer 120 and a nitride gate cap 125, all on top of asubstrate 110. Further, a pair of sidewall spacer may be disposed onopposite sides of the dummy gate 114, the dielectric layer 120, and thenitride 125. The dummy gate 114 may be on top of the substrate 110, thedielectric layer 120 may be formed on top of the dummy gate 114, thenitride 125 may be formed on the top of the dielectric layer 120, andthe pair of sidewall spacer 118 may be disposed on opposite sidewalls ofthe dummy gate 114.

The substrate 110 may include any semiconductor materials well known inthe art, such as, for example, undoped Si, n-doped Si, p-doped Si,single crystal Si, polycrystalline Si, amorphous Si, Ge, SiGe, SiC,SiGeC, Ga, GaAs, InAs, InP and all other III/V or II/VI compoundsemiconductors. Non-limiting examples of compound semiconductormaterials of the substrate 110 may include gallium arsenide, indiumarsenide, and indium phosphide. In an embodiment, the substrate 110 mayinclude a layered configuration such as, for example,silicon-on-insulator (SOI), SiC-on-insulator (SiCOI) or silicongermanium-on-insulator (SGOI). Also, the substrate 110 may be strained,unstrained or a combination thereof. Generally, the substrate 110 may beabout, but is not limited to, several hundred microns thick. In thepresent example, the substrate 110 may preferably be thin or very thinand have a thickness ranging from about 200 μm to about 1,000 μm.

Dummy gate 114 may be formed by first depositing a blanket layer ofpolysilicon directly on top of the substrate 110 followed by patterningthe blanket layer using masking and etching techniques well known in theart.

The dielectric layer 120 may be formed on top of the dummy gate 114. Thedielectric layer 120 may be formed from any of several known dielectricmaterials. Non-limiting examples include, for example, oxides, nitridesand oxynitrides of silicon. The dielectric layer 120 may be formed usingany of several known methods. The dielectric layers 120 may be about 150nm thick.

The nitride 125 may be deposited on the top of the dielectric layer 120by a chemical vapor disposition (CVD), or other suitable dispositionmethods. The nitride 125 may be materials, such as, titanium-nitride(TiN), titanium anti-reflective coating (TiARC), hafnium anti-reflectivecoating (hfARC), amorphous carbon (a-C), carbon (a-Si), or NBlock.

The dielectric layers 120 and 125 may also be deposited as blanketlayers on dummy gate material prior to patterning of dummy gates.

Next, the sidewall spacers 118 may be formed by depositing, or growing adielectric such as silicon dioxide, followed by an etch that removes thedielectric from the horizontal surfaces, while leaving the dielectric onthe sidewalls of the dummy gate 114. The sidewall spacers 118 mayinclude an oxide or nitride. The sidewall spacers 118 may have ahorizontal width ranging from about 3 nm to about 30 nm, with 10 nmbeing most typical. In an embodiment, the sidewall spacers 118 may bemade from nitride layer deposited using chemical vapor deposition (CVD).

Referring now to FIG. 2, a first flowable dielectric layer 130 isdeposited on top of the structure 100, according to embodiments. Thefirst flowable dielectric layer 130 may be deposited on the structure100 by, for instance, low pressure chemical vapor deposition (LPCVD),plasma-enhanced chemical vapor deposition (PECVD), flowable CVD (FCVD)or other techniques known in the art. Then, the first flowabledielectric layer 130 may be recessed to a level below a top surface ofthe nitride 125 using, for example, a wet etch or reactive-ion-etching(RIE). More specifically, the first flowable dielectric layer 130 may berecessed to expose an upper portion of the sidewall spacers 118. In anembodiment, the upper portion of the sidewall spacer exposed duringrecessing is at least 30% of a height of the sidewall spacer 118. In anembodiment, the upper portion of the sidewall spacer exposed duringrecessing is about 30% to about 90% of a height of the sidewall spacer118. In an embodiment, the upper portion of the sidewall spacer exposedduring recessing is about 40% to about 60% of a height of the sidewallspacer 118. Doing so will allow the formation of an additional spacer,as is described, in detail, below, with reference to FIG. 4. It shouldbe noted that while the exact recess depth is not critical, it isimportant that a sufficient height of the upper portion of the sidewallspacers be exposed to allow for the subsequent formation of theadditional spacer.

Referring now to FIG. 3, a conformal dielectric layer 140 may bedeposited on top of structure 100. The conformal dielectric layer 140may be made from a similar dielectric material as the sidewall spacers118 and/or the nitride 125, both described in detail above. Theconformal dielectric layer 140 may be deposited according to knowntechniques, such as, for example, chemical vapor deposition (CVD),Atomic Layer Deposition (ALD), plasma-enhanced chemical vapor deposition(PECVD), or some combination or variation thereof. The conformaldielectric layer 140 may have a thickness ranging from about 3 nm toabout 12 nm, however, the conformal dielectric layer 140 shall besufficiently thick to provide additional protection to the gate duringcontact trench etching. In an embodiment, the conformal dielectric layer140 may be a nitride deposited using ALD technique.

Referring now to FIG. 4, a demonstrative illustration of the structure100 after process steps of etching the conformal dielectric 140 to forma partial spacer 145. The partial spacers 145 may be formed by removinga portion of the conformal dielectric layer 140. More specifically, ananisotropic (directional) etching technique may be applied to removeportions of the conformal dielectric layer 140 from the horizontalsurfaces while leaving the conformal dielectric layer 140 on thesidewalls of the pair of dielectric spacers 118. For example, theconformal dielectric layer 140 may be removed from a top surface of thefirst flowable dielectric layer 130 and a top surface of the nitride125. The partial spacer 145 may have a horizontal width ranging fromabout 3 nm to about 10 nm, with 6 nm being most typical. In anembodiment, the conformal dielectric layer 140 may be deposited using an(Molecular Layer deposition) MLD technique. As referenced above, theheight or thickness of the first flowable dielectric layer 130, afterbeing recessed, dictates the location or position of the partial spacer145.

Next, a second flowable dielectric layer 160 may be blanket depositedabove the structure 100. A chemical mechanical polishing (CMP) techniquemay be applied to remove excess dielectric material, and ensure a cleanand flat surface in preparation for subsequent processing. In anembodiment, the CMP technique may polish the second flowable dielectriclayer 160 such that a top of the nitride 125 is exposed.

Referring now to FIG. 5, a demonstrative illustration of structure 100after process steps of a chemical mechanical polishing (CMP) techniqueand replacement of the dummy gate 114 with a metal gate, according to anembodiment. First, the CMP technique may be applied to expose the dummygate 114 in preparation for its subsequent removal. It should be notedthat the pair of sidewall spacers 118 may be simultaneously recessedduring the CMP technique.

Next, the dummy gate 114 may be removed from between the pair ofsidewall spacers 118 according to known techniques. In an embodiment,the dummy gate 114 may be removed using, for example, a wet etchingtechnique with either warm ammonium hydroxide (NH4OH) or warmTetramethylammonium hydroxide (TMAH).

Finally, a metal gate 150 may be formed in between the pair of sidewallspacers 118. In some embodiments, as illustrated, a gate dielectric 155may be first deposited formation of the metal gate 150. In anembodiment, the gate dielectric 155 may include a high-k dielectricmaterial. Furthermore, the metal gate 150 may include one or more layersmade from one or more work function metals depending on the application.

Referring now to FIG. 6, a demonstrative illustration of the structure100 after process steps of recessing the metal gate 150 and the gatedielectric 155 and formation of a gate cap 165. First, the metal gate150 and the gate dielectric 155 may be recessed selective to the pair ofsidewall spacers 118 according to known techniques, for example, wetetching or reactive ion etching. In an embodiment, the metal gate 150and the gate dielectric 155 may be recessed to a level at or about a topsurface of the flowable dielectric layer 130. Stated differently, theflowable dielectric layer 130 may be previously recessed to a height orthickness approximately equal to a pre-determined desired height of themetal gate 150 after being recessed. A gate cap 165 is then deposited ontop of the gate dielectric 155 and the metal gate 150 using knowdeposition techniques known in the art. In an embodiment, the gate cap165 may be deposited using, for example, chemical vapor deposition(CVD), atomic layer deposition (ALD), high density plasma (HDP),plasma-enhanced chemical vapor deposition (PECVD), or some combinationthereof. A chemical mechanical polishing technique may be applied toremove excess gate cap material before subsequent deposition of a thirdflowable oxide. After CMP, a third flowable dielectric layer 130 may beblanket deposited above the structure 100.

Referring now to FIG. 7, a final structure 100 is shown after forming aself-aligned contact 170 between two semiconductor devices. It should benoted that the thickness and height of the partial spacer 145 iscritical in that it must have a substantial volume to withstand contactetching and cause the self-aligned contact 170 to be laterally spacedaway from the gate 150 by a distance approximately equal to thethickness of the partial spacer 145.

The present invention provides fabrication of semiconductor deviceshaving an additional spacer for increasing the process margin forfabricating self-aligned contacts. One technique may include fabricatingthe additional spacer adjacent to an existing sidewall spacer of asemiconductor device. The additional spacer may alternatively bereferred to as a knee spacer. One embodiment by which to fabricate theadditional spacer and increase the process margin for fabricating selfaligned contacts, as described above, according to embodiments.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The terminology used herein was chosen to best explain the principles ofthe embodiment, the practical application or technical improvement overtechnologies found in the marketplace, or to enable others of ordinaryskill in the art to understand the embodiments disclosed herein.

What is claimed is:
 1. A semiconductor structure comprising: a gatestack located on a substrate; a first set of sidewall spacers located onopposite sidewalls of the gate stack; a first flowable dielectric layerlocated on the substrate and covering at a lower sidewall portion of thefirst set of sidewall spacers; a second set of sidewall spacers locatedadjacent to the first set of sidewall spacers and covering an upperportion of the first set of sidewall spacers, the second set of sidewallspacers have a bottommost surface located on a topmost surface of thefirst flowable dielectric layer; a second flowable dielectric layerlocated on the topmost surface of the first flowable dielectric layerand contacting outer sidewalls of the second set of sidewall spacers;and a contact located adjacent to at least one of the second set ofsidewall spacers and present in the first and second flowable dielectriclayers.
 2. The semiconductor structure of claim 1, wherein the substratehas a total thickness ranging from about 600 μm to about 800 μm.
 3. Thesemiconductor structure of claim 1, wherein the first flowabledielectric layer has a thickness ranging from about 10% to about 70% ofa height of the gate stack.
 4. The semiconductor structure of claim 1,wherein the contact is not in direct contact with the first set ofsidewall spacers and the second set of sidewall spacers keep the contactaway from contacting the first set of sidewall spacers.
 5. Thesemiconductor structure of claim 1, wherein a topmost surface of thecontact is coplanar with a topmost surface of the second flowabledielectric layer.
 6. The semiconductor structure of claim 1, wherein thegate stack comprises a gate cap located above and in direct contact witha metal gate.
 7. The semiconductor structure of claim 1, wherein saidgate stack comprises a gate dielectric and a metal gate, wherein atopmost surface of the gate dielectric is coplanar with a topmostsurface of the metal gate.
 8. The semiconductor structure of claim 1,wherein the bottommost surface of the second set of sidewall spacers iscoplanar with the topmost surfaces of the gate dielectric and the metalgate.
 9. The semiconductor structure of claim 1, wherein the bottommostsurface of the second set of sidewall spacers is coplanar with abottommost surface of a gate cap of the gate structure.
 10. Thesemiconductor structure of claim 1, wherein the first and second sets ofsidewall spacers comprise a same dielectric material.
 11. Thesemiconductor structure of claim 1, further comprising a third flowabledielectric layer located above the second flowable dielectric layer andthe gate stack, the third flowable dielectric layer further surroundingan upper portion of the contact.
 12. The semiconductor structure ofclaim 11, wherein a topmost surface of the third flowable dielectriclayer is coplanar with a topmost surface of the contact.
 13. Thesemiconductor structure of claim 1, wherein the contact is T-shaped. 14.The semiconductor structure of claim 13, wherein a portion of thecontact directly contacts a topmost surface of each of the first andsecond sets of sidewall spacers that are located on one side of the gatestack.
 15. The semiconductor structure of claim 1, wherein the substrateis a semiconductor substrate.
 16. The semiconductor structure of claim1, wherein said gate stack comprises a gate dielectric and a metal gate,wherein a topmost surface of the gate dielectric is coplanar with atopmost surface of the metal gate, and the topmost surfaces of the gatedielectric and the metal gate are both coplanar with a topmost surfaceof the first flowable dielectric layer.